<!DOCTYPE html>
<html>
  <head>
    <title>
      waveshaper.html
    </title>
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <script src="../../resources/audit-util.js"></script>
    <script src="../../resources/audit.js"></script>
  </head>
  <body>
    <script id="layout-test-code">
      let audit = Audit.createTaskRunner();

      let sampleRate = 44100;
      let lengthInSeconds = 4;
      let numberOfRenderFrames = sampleRate * lengthInSeconds;
      let numberOfCurveFrames = 65536;
      let inputBuffer;
      let waveShapingCurve;

      let context;

      function generateInputBuffer() {
        // Create mono input buffer.
        let buffer =
            context.createBuffer(1, numberOfRenderFrames, context.sampleRate);
        let data = buffer.getChannelData(0);

        // Generate an input vector with values from -1 -> +1 over a duration of
        // lengthInSeconds. This exercises the full nominal input range and will
        // touch every point of the shaping curve.
        for (let i = 0; i < numberOfRenderFrames; ++i) {
          let x = i / numberOfRenderFrames;  // 0 -> 1
          x = 2 * x - 1;                     // -1 -> +1
          data[i] = x;
        }

        return buffer;
      }

      // Generates a symmetric curve: Math.atan(5 * x) / (0.5 * Math.PI)
      // (with x == 0 corresponding to the center of the array)
      // This curve is arbitrary, but would be useful in the real-world.
      // To some extent, the actual curve we choose is not important in this
      // test, since the input vector walks through all possible curve values.
      function generateWaveShapingCurve() {
        let curve = new Float32Array(numberOfCurveFrames);

        let n = numberOfCurveFrames;
        let n2 = n / 2;

        for (let i = 0; i < n; ++i) {
          let x = (i - n2) / n2;
          let y = Math.atan(5 * x) / (0.5 * Math.PI);
        }

        return curve;
      }

      function checkShapedCurve(buffer, should) {
        let inputData = inputBuffer.getChannelData(0);
        let outputData = buffer.getChannelData(0);

        let success = true;

        // Go through every sample and make sure it has been shaped exactly
        // according to the shaping curve we gave it.
        for (let i = 0; i < buffer.length; ++i) {
          let input = inputData[i];

          // Calculate an index based on input -1 -> +1 with 0 being at the
          // center of the curve data.
          let index = Math.floor(numberOfCurveFrames * 0.5 * (input + 1));

          // Clip index to the input range of the curve.
          // This takes care of input outside of nominal range -1 -> +1
          index = index < 0 ? 0 : index;
          index =
              index > numberOfCurveFrames - 1 ? numberOfCurveFrames - 1 : index;

          let expectedOutput = waveShapingCurve[index];

          let output = outputData[i];

          if (output != expectedOutput) {
            success = false;
            break;
          }
        }

        should(
            success, 'WaveShaperNode applied non-linear distortion correctly')
            .beTrue();
      }

      audit.define('test', function(task, should) {
        // Create offline audio context.
        context = new OfflineAudioContext(1, numberOfRenderFrames, sampleRate);

        // source -> waveshaper -> destination
        let source = context.createBufferSource();
        let waveshaper = context.createWaveShaper();
        source.connect(waveshaper);
        waveshaper.connect(context.destination);

        // Create an input test vector.
        inputBuffer = generateInputBuffer();
        source.buffer = inputBuffer;

        // We'll apply non-linear distortion according to this shaping curve.
        waveShapingCurve = generateWaveShapingCurve();
        waveshaper.curve = waveShapingCurve;

        source.start(0);

        context.startRendering()
            .then(buffer => checkShapedCurve(buffer, should))
            .then(task.done.bind(task));
      });

      audit.run();
    </script>
  </body>
</html>
